Characteristics of soil profile COsub2/sub concentrations in karst areas and their significance for global carbon cycles and climate change

摘要

CO2 concentrations of 21 soil profiles were measured inZhaotong City, Yunnan Province. The varying characteristics of soil profileCO2 concentrations are distinguishable between carbonate andnoncarbonate areas. In noncarbonate areas, soil profile CO2concentrations increase and show significant positive correlations with soildepth. In carbonate areas, however, deep-soil CO2 concentrationsdecrease and have no significant correlations with soil depth. Soil organiccarbon is negatively correlated with soil CO2 concentrations innoncarbonate areas. In carbonate areas, such relationships are not clear.This means that the special geological process in carbonate areas – carbonatecorrosion – absorbs part of the deep-soil-profile CO2. Isotope and soilpH data also support such a process. A mathematical model simulating soil profile CO2 concentration wasproposed. In noncarbonate areas, the measured and the simulated values arealmost equal, while the measured CO2 concentrations of deep soils areless than the simulated in carbonate areas. Such results also indicate theoccurrence of carbonate corrosion and the consuming of deep-soil CO2 incarbonate areas. The decreased CO2 concentration was roughly evaluatedbased on stratigraphic unit and farming activities. Soil pH and the purityof CaCO3 in carbonate bedrock deeply affect the corrosion. Thecorrosion in carbonate areas decreases deep-soil CO2 greatly(accounting for 5.2 %–66.3 % with average of 36 %) and naturally affectsthe soil CO2 released into the atmosphere. Knowledge of this process isimportant for karst carbon cycles and global climate changes and it may bea part of the “missing carbon sink”.